The influence of particle concentration and polarizing field on the resonant behaviour of magnetic fluids

Starting from the Landau-Lifshitz equation, with resonant frequency f0 ω0/2π, it is demonstrated that, in the case of a magnetic fluid, the measured resonant frequency, fres is always different from f0, except for the case of pure resonance (i.e. zero damping parameter of Landau-Lifshitz equation) where fres = f0. It is also shown that fres and the corresponding maximum absorption frequency, fmax, are different, thus supporting the deductions of Scaife, who arrived at this conclusion using an alternative theoretical approach. Furthermore, based on complex magnetic susceptibility measurements, over the frequency range 100 MHz - 6 GHz, the dependence of the ratio fmax/fres on an external polarizing magnetic field, Hpol, over the approximate range 0 and 1.3 kOe and on particle concentration has been examined for different magnetic fluid samples. It is demonstrated how the ratio fmax/fres tends to unity both by (i) increasing the polarizing field and (ii) decreasing the particle concentration of the samples